This invention is based on Japanese Patent Application No. 2000-169273, filed Jun. 6, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present application relates to an engine control arrangement for controlling a watercraft, and more particularly relates to an engine management system that controls engine speed in order to reduce noise.
2. Description of the Related Art
Watercraft, including personal watercraft and jet boats, are often powered by at least one internal combustion engine having an output shaft arranged to drive one or more water propulsion devices. Occasionally, engine revving is conducted out of the water in order to test the engine or to use exhaust pressure to drain salt water that has entered the engine during cruising.
Unfortunately, since there is no water resistance applied to the propulsion device when revving the engine out of the water, the engine speed may easily reach or exceed a maximum safe speed when the throttle is slightly applied, which causes extremely loud noise.
The present application is directed to an engine control arrangement of the type used to power a watercraft, which controls the engine speed and prevents the engine from revving too high when out of the water, thus preventing excessively loud noise.
One aspect of the preferred embodiments is an engine speed control system for a watercraft that is propelled by a stream of water generated by a propulsion unit driven by an engine. The engine control system comprises means for detecting whether the propulsion unit is generating a stream of water. The system also comprises a controller responsive to the means for detecting, the controller limiting the maximum engine speed to a first speed when the propulsion unit is generating the stream of water, the controller limiting the maximum engine speed to a second speed, lower than the first speed, when the propulsion unit is not generating the stream of water.
In one preferred embodiment of this first aspect, the means for detecting comprises a first sensor that senses ambient atmospheric pressure and a second sensor that senses a pressure responsive to the movement of the stream of water. The means for detecting compares the ambient atmospheric pressure and the pressure responsive to the movement of the stream of water to determine whether the stream of water is being generated by the propulsion unit.
In one particularly preferred embodiment, the propulsion unit includes an inlet that receives water, and the second sensor is positioned in the inlet such that the pressure sensed by the second sensor decreases with increasing water flow and increases with decreasing water flow.
In an alternative particularly preferred embodiment, the propulsion unit includes an outlet that conveys the stream of water generated by the propulsion unit, and the second sensor is positioned in the outlet such that the pressure sensed by the second sensor increases with increasing water flow and decreases with decreasing water flow.
In an alternative embodiment, the means for detecting comprises a sensor that responds to the speed of the watercraft to determine whether the stream of water is being generated by the propulsion unit.
In accordance with a particular aspect of the preferred embodiment, the controller reduces the engine speed to the second speed only after the controller determines that the propulsion unit is not generating the stream of water for a predetermined time duration. For example, the predetermined time duration is advantageously at least 5 seconds.
In one exemplary embodiment, the first speed is 7,000 revolutions per minute, and the second speed is 4,000 revolutions per minute.
A second aspect of the preferred embodiments is a method for reducing engine speed and thereby reducing engine noise of a watercraft propelled by a stream of water generated by a propulsion unit driven by an engine when the watercraft is out of the water. The method comprises sensing whether the watercraft is out of the water, controlling the engine speed to a first maximum speed when the watercraft is in the water, and controlling the engine speed to a second maximum speed when the watercraft is out of the water, the second maximum speed lower than the first maximum speed.
In one preferred embodiment of this second aspect, the sensing step comprises comparing a first pressure with a second pressure to determine whether water is flowing through the propulsion unit. In a particularly preferred embodiment, the first pressure is ambient atmospheric pressure, and the second pressure is determined by the flow of water through the propulsion unit.
In a first alternative of this particularly preferred embodiment. the second pressure is measured at an inlet to the propulsion unit, the second pressure decreasing with increasing flow of water and decreasing with increasing flow of water.
In a second alternative of this particularly preferred embodiment, the second pressure is measured at an outlet to the propulsion unit, the second pressure decreasing with decreasing flow of water and increasing with increasing flow of water.
In an alternative embodiment, the sensing step comprises sensing the speed of the watercraft to determine whether water is flowing through the propulsion unit.
In particular aspects of the method, the engine speed is controlled to the second speed only after the method determines that the propulsion unit is not generating the stream of water for a predetermined time duration. In an exemplary embodiment of the method, the predetermined time duration is at least 5 seconds.
In particular embodiments of the method, the first speed is 7,000 revolutions per minute, and the second speed is 4,000 revolutions per minute.